I was thinking about this the other day on another thread. The Nebraska DC is Bo's brother, which would make a lateral move a bit more unlikely, but not out of the question imo. Carl Pelini doesn't get the credit for what Nebraska's defense is doing, Bo does, so the idea of moving to another high profile place like ND and getting all the credit might appeal to him. The same could be said of Alabama's DC, for that matter. Same reasoning.
Whatever the case, if Kelly is hired, or any coach with more of an offensive leaning for that matter, I hope he give his DC some latitude to hire his own assistants. Not complete carte blanche because he's still the head coach and ultimately the responsibility falls on him, but a good amount. That way they can actually get a defensive system in place, not just a collection of coaches with some name recognition, which is what I think we saw under Charlie somewhat.